Preparation of a monoclonal antibody specific for a 48-kDa protein from mitochondrial nucleoids of the yeast, Saccharomyces cerevisiae.

Monoclonal antibodies (mAbs) were raised against yeast mitochondrial nucleoids (mt-nucleoids). In an analysis by a combination of immunofluorescence microscopy and staining with 4',6-diamidino-2-phenylindole (DAPI), one of them, designated YMN-1, distinctly stained mt-nucleoids, which were visible as dots, in spheroplasts and in isolated mitochondria. However, staining of isolated mt-nucleoids was rather weak. YMN-1 mAb recognized a 48-kDa protein in immunoblots of both mitochondrial and mt-nucleoid proteins. The 48-kDa protein was a minor component of mt-nucleoid proteins and was separated from extract of both mitochondria and mt-nucleoids by immunoaffinity chromatography. The affinity-purified 48-kDa protein reassociated with mt-nucleoids when mixed with isolated mt-nucleoids, as monitored by immunofluorescence microscopy. The results suggest that a large amount of 48-kDa protein is associated with mt-nucleoids in vivo, and that lysis of mitochondria by the treatment with detergent releases a considerable amount of this protein from mt-nucleoids during the isolation of mt-nucleoids.